This invention relates to an intake/exhaust type combustion equipment, and more particularly to an intake/exhaust type combustion equipment adapted to use outdoor air as combustion air and discharge exhaust gas produced by a burner to the outdoors.
A typical intake/exhaust type combustion equipment which has been conventionally known in the art is disclosed in Japanese Patent Application Laid-Open Publication No. 302712/1993, of which the disclosure is incorporated herein by reference. The conventional intake/exhaust type combustion equipment disclosed, which was proposed by the assignee, includes a pot-type burner for combustion arranged in a frame, a fuel feed means for feeding fuel to the burner and a combustion air feed fan arranged in an intake passage for feeding the burner with combustion air introduced from the outdoors. The intake/exhaust type combustion equipment also includes a heat exchanger arranged in an intermediate portion of an exhaust passage which permits exhaust gas to be guided therethrough to the outdoors and constructed so as to carry out heat exchange between combustion gas produced in the burner and indoor air, and a convection fan for flowing indoor air against the heat exchanger.
Another conventional intake/exhaust type combustion equipment which is constructed so as to lead out intake and exhaust passages to the outdoors is disclosed in Japanese Patent Application Laid-Open Publication No. 128623/1996, of which the disclosure is incorporated herein by reference. In the intake/exhaust type combustion equipment, which was likewise proposed by the assignee, an intake pipe and an exhaust pipe are configured into a double-pipe structure.
Also, a further conventional intake/exhaust type combustion equipment is disclosed in Japanese Patent Application Laid-Open Publication No. 302712/1993, of which the disclosure is incorporated herein by reference. The combustion equipment disclosed is so constructed that the amount of fuel fed from a fuel feed means and a rotational speed of a combustion air feed fan are varied depending on the amount of combustion. In the combustion equipment, an increase in combustion is attained by increasing a rotational speed of the combustion air feed fan and a reduction in combustion is carried out by reducing the rotational speed.
When an intake/exhaust type combustion equipment which has a burner incorporated therein is constructed so as to use indoor air as combustion air, combustion operation of the combustion equipment permits air fed to the burner to be readily heated to a temperature at a level of a temperature in a room in which the equipment is placed, resulting in density of the air during combustion operation of the combustion equipment being kept substantially constant, so that balance between the amount of combustion and the amount of oxygen required for keeping the combustion may be maintained to permit the equipment to provide stable combustion.
In the combustion equipment, feed of air to a burner by means of a combustion air feed fan is carried out while varying a rotational speed of a motor for driving the fan to control the amount of combustion air fed to the burner. For this purpose, the fan driving motor has a revolving shaft mounted thereon with a rotational speed detecting sensor, to thereby control the fan driving motor so as to ensure that the motor may be constantly operated at a desired rotational speed. Nevertheless, such arrangement often fails to constantly ensure that oxygen in an amount actually required for combustion is fed to the burner. This fails to maintain proper balance between the amount of fuel fed to the burner and the amount of oxygen contained in air fed thereto by means of the combustion air feed fan, leading to problems such as incomplete combustion due to deficiency of oxygen, malfunction of the combustion equipment due to oversupply of oxygen and the like.
In order to solve the problems, in the prior art, the amount of combustion air fed to the burner by the combustion air feed fan is set to be above a level which permits proper balance between a rotational speed of the combustion air feed fan or the amount of combustion air fed to the burner and the amount of fuel fed thereto, to thereby prevent production of carbon monoxide (CO) gas due to deficiency of oxygen. However, this essentially causes oversupply of oxygen to the burner. Such oversupply is amplified in combustion operation of the combustion equipment under low-temperature conditions which cause air density varied depending on a temperature to be increased.
Oversupply or excess of oxygen causes only a flame reduced in height to be formed during combustion operation of the combustion equipment, leading to malfunction of a safety unit which is arranged in the combustion equipment and has a flame sensor incorporated therein. Also, incomplete combustion in the burner due to deficiency of oxygen causes adhesion of carbon to the burner, leading to a deterioration in thermal efficiency. Further, even when the amount of air is set above a level required for the proper balance as described above, the combustion equipment, which it is operated on a highland of which the height above the sea level is highly increased, causes incomplete combustion due to deficiency of oxygen, because an oxygen concentration is reduced at such a highland.